1. Technical Field of the Invention
This invention relates to a vehicle lamp having a reflector for reflecting light from a light source and more particularly to a vehicle lamp whose reflector has a reflective surface coated with a reflective coating film containing aluminum flakes.
2. Description of the Related Art
There are generally known reflectors as members for use in forming vehicle lamps such as a reflector made by aluminum deposition provided on the surface of a reflector base so as to form a reflective surface with an aluminum deposited film (hereinafter called an aluminum deposited reflector), and a reflector made by applying a reflective coating to a reflector base so as to form a reflective surface with a reflective coating film (hereinafter called a reflective coated reflector).
As shown in FIG. 7, the aluminum deposited reflector is utilized mainly for a lamp, such as a headlamp, which has a greater luminous intensity because the aluminum deposited reflector has a specular reflectance of 50% or higher (the percentage of reflected rays of light at the incident and reflected angles equal to each other with respect to the incident ray) and a center luminous intensity (the maximum luminous intensity obtained by turning on a bulb of 12 V, 27 W and 400 lm for a parabolic reflector of F25) of 9,000 cd or greater when a predetermined bulb arranged for a parabolic reflector having a configuration of FIG. 8 is lighted.
On the other hand, the reflective coated reflector is utilized for a beacon lamp and the like, which do not have as great a luminous intensity because the reflective coated reflector has a specular reflectance of about 40% or lower and a center luminous intensity of about 8,000 cd or less (200-8,000 cd). As is obvious from FIG. 7, the specular reflectance has a substantially proportional relationship to the center luminous intensity.
Further, although the aluminum deposited reflector provides a greater luminous intensity than the reflective coated reflector, the aluminum deposited reflector is costly because it requires large deposition facilities, many manufacturing steps and a great deal of time for production. On the contrary, although a great luminous intensity is not obtainable with the reflective coated reflector, it is less costly and can be manufactured efficiently, because it only requires simple coating facilities, and the steps of applying a reflective coating prepared by mixing a resin as a binder and aluminum flakes, and adding a volatile solvent to the mixture so as to adjust the viscosity.
In the case of recent beacon lamps such as tail lamps, clearance lamps, turn-signal lamps and the like, the interior of a lamp chamber is arranged so as to be seen through without providing any step for a front lens in order to make the lamps look solid. Consequently, the aluminum deposited reflector offering greater luminance instead of the reflective coated reflector, is employed for emphasizing the solidity. When the luminous intensity is too great for a specific beacon lamp as a result of using the aluminum deposited reflector, applying a smoke top coat onto the aluminum deposited surface or forming an emboss on the reflector base surface where the aluminum deposited film is formed, may be employed for reducing the luminous intensity whereby to provide a lower suitable luminous intensity for the beacon lamp.
Since the luminous intensity obtainable from the conventional reflective coated reflector is limited, such conventional reflective coatings are not used in the aforementioned beacon lamp of the see-through type, and thus, there is a problem arising from the necessity of using the expensive aluminum deposited reflector for a lamp which needs a substantially great luminous intensity.
In the aforementioned beacon lamp of the see-through type, it has been deliberately contrived to decrease the luminous intensity obtainable from the original aluminum deposited film as discussed above, resulting in the problem that the beacon lamp becomes costly to the extent that special labor and time are needed to make a reflector for this purpose.
With respect to the problems above, the present inventor has studied the possibility of increasing the center luminous intensity (specular reflectance) of the reflective coated reflector, as greater luminance may have the effect of providing more solidity and increasing the center luminous intensity (specular reflectance) of the reflective coated reflector without having to contrive a means of lowering the luminous intensity of the reflector.
The reflective coating film used to form the reflective surface of a reflector is structured as shown in FIG. 9(a) so that an aluminum flake layer 3 in which aluminum flakes 4 having a mean particle diameter of 3 xcexcm or greater and a thickness of 0.1 xcexcm or greater are lined up continuously and formed in the surface layer portion of a resin layer 2 as a binder adhering to the surface of a reflector base 1, the aluminum flake layer 3 forming a reflective surface for reflecting light.
The reflective coated reflector is formed by mixing the resin 2 as a binder and the aluminum flakes 4, and adding a volatile solvent to the mixture so as to adjust the viscosity to a predetermined degree. In order to increase floatability with respect to the resin 2 as a binder, stearic acid is made to adhere to the aluminum flakes 4 in the reflective coating beforehand. Consequently, the aluminum flakes 4 are kept floating within the liquid resin (layer) 2 in the coating (coating film) immediately after the coating is applied to the reflector base 1 as shown in FIG. 9(b). As the drying and hardening of the resin (layer) 2 progress, the aluminum flakes 4 are piled up and the aluminum flake layer 3 appears to be formed in the surface layer portion of the film as shown in FIG. 9(a).
Therefore, the present inventor reasoned that the center luminous intensity be increased by increasing the smoothness of the surface of the aluminum flake layer 3 and studied a method of increasing the surface smoothness of the aluminum flake layer 3.
First, the size (particle diameter) of the aluminum flakes 4 to be mixed in was reduced. As shown in FIG. 10, the finer (the smaller of the particle diameters) the aluminum flake, the greater the center luminous intensity became to some extent. However, the luminous intensity did not reach 8,000 cd.
Then it was attempted to reduce the thickness of the aluminum flake 4 without changing the size (particle diameter) of the aluminum flake 4 to be mixed in. As shown in FIG. 11, the thinner the aluminum flake 4, the greater the center luminous intensity became. Thus, a center luminous intensity (specular reflectance) of not less than 8,000 cd was obtained, which had previously not been obtainable from any one of the conventional reflective coated reflectors.
Attention was also focussed on the softening point of the resin (layer) 2 as a binder for use in forming the reflective coating film and resins different in the softening point were used. It was proved that the lower the softening point of the resin, the greater the center luminous intensity became (see FIG. 5).
An object of the present invention, in view of the foregoing problems pertaining to the prior art and the present inventor""s reasoning, is to provide a vehicle lamp fitted with a reflective coated reflector capable of obtaining a greater center luminous intensity (specular reflectance) that has not been obtainable from conventional reflective coated reflectors.
In order to accomplish the above object, a vehicle lamp comprises a light source, a reflector disposed behind the light source, used to reflect light from the light source forward, and a front lens disposed in front of the light source, wherein the reflective surface of the reflector is formed with a luminance reflective coating film having a center luminous intensity of 8,000-13,000 cd, the luminance reflective coating film being formed by applying a luminance reflective coating to a reflector base and drying the coating, the luminance reflective coating being prepared by mixing a binder and thin aluminum flakes having a thickness of 0.01-0.06 xcexcm with stearic acid adhering to the flakes, and making the coating have a predetermined viscosity by using a solvent.
An aluminum flake layer with the piled-up aluminum flakes is formed in the surface layer portion of the luminance reflective coating film and this aluminum flake layer forms the reflective surface for reflecting light. Since the aluminum flakes (0.01-0.06 xcexcm in thickness) mixed in the luminance reflective coating film are thinner than the aluminum flakes (0.1 xcexcm or greater in thickness) mixed in the conventional reflective coating film, irregularities of the aluminum flake layer are decreased. Moreover, the aluminum flakes are lighter than the bulk aluminum flakes in the luminance reflective coating (film) immediately after being applied to the reflector, and since the stearic acid is sticking onto the surface of each aluminum flake, the aluminum flakes are easily kept afloat within the coating film (the resin layer) and also readily piled up in the surface layer portion of the luminance reflective coating film as the coating film (the resin layer) dries and hardens. Therefore, the aluminum flake layer is extended in uniform thickness along the surface of the luminance reflective coating film, and the surface of the aluminum flake layer is smoothed with the effect of increasing the specular reflectance, whereby a greater center luminous intensity (of 8,000-13,000 cd) that has been unobtainable from the conventional reflective coated reflector can be obtained.
In other words, although uniformity as well as smoothness of the thickness of the aluminum flake layer increases while the thickness of each aluminum flake remains at less than 0.01 xcexcm, the center luminous intensity (specular reflectance) is decreased because light is caused to pass through the aluminum flakes. If the thickness of each aluminum flake exceeds 0.06 xcexcm, a gap will be produced between the aluminum flakes in the aluminum flake layer, and the thickness of the aluminum flake layer will lack uniformity, which results in decreasing not only the smoothness of the surface of the aluminum flake layer but also the center luminous intensity (specular reflectance).
If the thickness exceeds 0.06 xcexcm, the floatability of the aluminum flakes with respect to the resin will lower slightly and the percentage having the aluminum flakes piled up in the surface layer portion will also lower, thus causing the center luminous intensity (specular reflectance) to decrease. Therefore, it is desirable to set the thickness from 0.01 to 0.06 xcexcm for increasing the center luminous intensity (specular reflectance).
Further, the softening point of a resin which is the binder used to form the luminance reflective coating film should range from 95 to 140xc2x0 C., and preferably range from 100-120xc2x0 C.
With respect to forming a uniform aluminum flake layer in the surface layer portion of the luminance reflective coating film by increasing the floatability of the aluminum flakes as one of the factors for increasing the center luminous intensity (specular reflectance), it is preferred that the softening point of the resin layer (resin acting as an aluminum-flake binder) forming the (lower layer portion of the) luminance reflective coating film is lower. If, however, the softening point of the resin is lower than 95xc2x0 C., the resin layer will become softened when the film temperature reaches over 95xc2x0 C. and the aluminum flake layer will crack. If the softening point of the resin layer exceeds 140xc2x0 C., the aluminum flakes will not be able to float satisfactorily in the resin as a binder in the luminance reflective coating film thus applied because the high viscosity of the resin. In addition, the aluminum flakes are intermingled in the resin layer of the hardened luminance reflective coating film and this also results in decreasing the center luminous intensity (specular reflectance). Therefore, the softening point of the resin forming the luminance reflective coating film should preferably be not lower than 95xc2x0 C. in view of heat resistance and not higher than 140xc2x0 C. in order to increase the specular reflectance. It is desirable to use a resin as a binder having a softening point of from 100 to 120xc2x0 C. so as to secure resistance against heat at 95xc2x0 C. and a center luminous intensity of not less than 100 cd in particular.
In a vehicle lamp, the front lens may be provided with a see-through portion through which the reflective surface of the reflector is seen. Since the reflector with greater luminance is seen through the see-through portion of the front lens, a feeling of depth (solidity) is emphasized.